1. Field of the Invention
The present invention relates to storage capacity change of devices specified by a host device.
2. Description of the Related Art
A well-known logical volume is of a type dynamically allocated with a substantial area in accordance with an increase or decrease of the number of the substantial areas allocated to the logical volume. Such a logical volume is hereinafter referred to as “virtual volume”. An example includes Patent Document 1 (JP-A-2003-015915). With the technology of this type, out of the storage capacity of a virtual volume, the storage capacity of one or more substantial areas allocated to the virtual volume is entirely configured from the physical storage space of a storage system. Such entire storage capacity of the substantial areas(s) is referred to as “substantial capacity”. The substantial capacity of the virtual volume is changed in accordance with an increase or decrease of the number of the substantial areas allocated to the virtual volume. Note here that the physical storage space is a storage space provided by a parity group (hereinafter, sometimes referred to as “PG”). The PG is configured by one or more physical storage devices, e.g., hard disk drive or flash memory.
A storage system can be generally configured mainly by a controller and a storage device group. The storage device group is configured by one or more physical storage devices described above. The controller provides devices to a host device, e.g., a host or any other controller, and such devices are exemplified by logical units (LUs). The LUs are respectively associated with logical volumes under the management of the controller. When the host device forwards an access request, i.e., write request or read request, with a specification of LU, any logical volume associated with the LU is accessed. The logical volume associated with the LU as such may be virtual or general. The general volume is a logical volume formed based on the above-described physical storage space.
The controller may be provided with a capacity change command, i.e., command for increasing or reducing the storage capacity, with a specification of LU from the host device or any other device. The storage capacity of the LU notified to the host is generally the storage capacity of the logical volume associated with the LU. Therefore, changing the storage capacity of the LU means generally to change the storage capacity of the logical volume associated with the LU.
The concern here is that the technology of changing the storage capacity of a logical volume itself has not yet been proposed.
In consideration thereof, in response to a capacity change command, the controller increases or decreases the number of the logical volumes associated with any specified LU, thereby changing the capacity of the LU. With a specific example of FIG. 1, when a capacity increase command specifying an LU#100 is provided, in response thereto, the controller increases the number of the general volumes associated with the LU#100 from 1 to 3. More in detail, the controller combines the general volumes #2 and #3 to the general volume #1 associated with the LU #100. This accordingly enables to increase the storage capacity of the LU while the host device is being in operation.
However, this technology has the following problems.
1. The capacity change is made in accordance with an increase or decrease of the number of the general volumes associated with an LU.
2. At the time of capacity increase, there may be a case where there is no general volume. If this is the case, there needs to be a newly created general volume(s).
Such problems are those observed when logical volumes associated with the LU are general volumes. However, even if general volumes are replaced with virtual volumes, similar problems may occur.